Optoelectronic devices such as light emitting diodes (LEDs) and laser diodes have numerous applications and are growing in popularity. LEDs—including those outputting white and other colors of light—are used, for example, for general and automotive illumination, for backlights in liquid crystal and other displays, for high color rendering index devices, and for color mixing devices. Laser diodes are used, for example, in various communication applications, including transmitters for optical fiber communications systems and single-mode pump diodes for fiber amplifiers. LEDs and laser diodes are solid state devices each having a P-N junction semiconductor diode that emits radiation (e.g., infrared radiation, visible radiation, ultraviolet radiation, and so on) responsive to application of electrical current.
In the illumination context, usage of LEDs is increasing relative to incandescent and other lighting technologies because LEDs generally have longer service life, better efficiency in converting electrical energy into radiation energy in the visible spectral range, and lower thermal emission characteristics. LED lamps are considerably more robust than other conventional (e.g., incandescent, halogen, fluorescent, or high intensity discharge) lamps because they lack filaments and do not require fragile glass exterior casings. Instead, a LED lamp is typically disposed in or under a covering of an encapsulant material and optional lens (which may be integrated with the encapsulant), with such encapsulant and optional lens typically being fabricated of durable polymeric materials. Further advantages of LEDs are that they have rapid turn-on time and generate less heat per lumen of light output relative to traditional lighting products.
There are currently three methods for producing LEDs that emit white light. The first and second methods use a single blue, violet or UV LED die that emits a single wavelength of radiation. The first method utilizes a phosphoric coating deposited on the LED die, with the phosphor serving to convert portions of the light into longer wavelengths that lead to the perception of white light. The second method also uses a phosphor for the same purpose, but in the form of a phosphoric layer disposed well above the LED die—e.g., on the outer surface of an encapsulant, or between an encapsulant and lens of a LED package. The third method eliminates the need for phosphors; instead, it employs independent red, blue, and green dies in the same package that emits light perceived as white in color when all three dies are powered.
Numerous applications for LEDs and laser diodes would benefit from greater flux density; however, various considerations thermal and packaging constraints have limited the ability flux density output of conventional optoelectronic devices. It would be desirable to achieve greater flux density from an optoelectronic device without causing such device to overheat. It would be even more desirable if such result could be obtained with an electrically isolated thermal path, to ensure smooth device operation at high current and/or high temperature operating states. It would be further desirable to attain high flux density without making the resulting device more susceptible to electrostatic discharge or voltage aberrations.
With regard to device packaging, it would be desirable to reduce the spatial footprint of structure required to support the emitting region of an LED—particularly in the context of multi-LED devices. For example, the closer that independent LED dies (e.g., red, blue, and green dies) are placed in proximity to one another in a multi-LED device, the more closely that the resulting combination of dies approximates a point source, thus enhancing the perception of color mixing and concomitantly reducing a viewer's ability to perceive discrete color emissions from adjacent dies emitting distinct wavelengths. Packaging and thermal constraints, however, currently limit the ability for multiple LEDs to operate at high flux densities while being disposed very close together.
Conventional optoelectronic device packages require numerous components and component assembly steps. To promote efficiency and minimize the potential for part mishandling and/or fabrication errors, it would be desirable to minimize the number of discrete components and assembly steps required to fabricate functional optoelectronic device packages.
LEDs, especially gallium nitride-based LEDs, are particularly susceptible to damage to electrostatic discharge or other application of a reverse bias voltage to the anode and cathode. To prevent damage to a LED due to electrostatic discharge, a secondary electrostatic discharge (ESD) diode operating in the breakdown region (i.e., in a conductive state) is typically connected in parallel with the LED. A normal forward bias voltage applied to the terminals of the LED flows through the P-N junction of such LED and generates light. When an abnormal reverse voltage appears or there is an electrostatic discharge, excess voltage is discharged through the secondary ESD diode operating in the breakdown mode. Since the discharge path goes through the secondary diode rather than the LED, the LED will not be damaged due to electrostatic discharge or abnormal voltage. Although such parallel ESD diode protection system is capable of minimizing damage to the LED, the addition of ESD protection makes manufacture of a LED package more difficult and costly, and undesirably increases the footprint of a LED package. It would be desirable to provide ESD protection in an optoelectronic device package while minimizing these concerns.
Following assembly, optoelectronic packages, such as LED packages, are typically performance tested and “binned” (i.e., sorted) according to ranges of dominant wavelength and brightness. Such binning permits intensity and/or color matching between various packages to be used in a particular product or product line. Testing and binning can consume substantial resources of labor and or equipment. It would be desirable to permit numerous optoelectronic device packages to the tested and binned simultaneously.
Accordingly, there is a continuing need in the art for improved optoelectronic device packages and methods for making the same.